1. Field of the Invention
The present invention relates to a differential gear unit assembled in a trans-axle casing, and more particularly to a support structure of the differential gear unit in the trans-axle casing.
2. Description of the Prior Art
In a differential gear unit assembled in a trans-axle casing having an open end closed by a removable cover member fastened thereto, the outer case of the differential gear unit has a pair of side-journals rotatably supported by a pair of tapered roller bearings which are carried on a pair of axially spaced carrier portions of the trans-axle casing. In such a conventional support structure of the differential gear unit, the carrier portions of the trans-axle casing each are formed therein with a semi-cylindrical bore, and the tapered roller bearings each are coupled with the semi-cylindrical bore of the carrier portion and retained in place by means of a retainer member secured to the carrier portion. For the purpose of eliminating such additional parts as the retainer members, it has been proposed to form a cylindrical bore in the carrier portions of the trans-axle casing respectively for supporting therein the tapered roller bearing in a fluid-tight manner. In this case, the cylindrical bore of the carrier portion is formed, in general, at its intermediate portion with an annular groove in which a snap ring is engaged to retain the tapered roller bearing in an axial direction. For engagement with the annular groove, the snap ring must be inserted into the cylindrical bore of the carrier portion from its one end. If an internal surface of the cylindrical bore is damaged by the snap ring in the course of insertion into the carrier portion, unexpected leakage of lubricating oil will occur at the carrier portions. Moreover, the snap ring must be compressed radially inwardly for insertion into the cylindrical bore of the carrier portion. In the case that the annular groove is formed as a shallow annular groove to facilitate insertion of the snap ring, the engagement face of the snap ring with a side wall of the groove is inevitably reduced. As a result, the snap ring is apt to be deformed and removed due to an increase of the thrust force acting thereon from the tapered roller bearing.